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The thing that nobody has illustrated properly is that the balloon is just a way to hold the outside edge of the parabola taunt, there's a flat metalized sheet
by mikewarot 3y ago
The thing that nobody has illustrated properly is that the balloon is just a way to hold the outside edge of the parabola taunt, there's a flat metalized sheet inside, that basically cuts the interior volume in half, that gets stretched into a parabola by differential pressure, forming the reflector.
You then put your feed horn on the outside of the balloon at the right place, aimed at the parabola inside, and you have a high gain antenna.
I found an image, note the 2 hoses in the lower left, one for each half, to allow regulating the pressure differential.
https://www.researchgate.net/profile/Stella-Parisi/publication/261795695/figure/fig50/AS:614305368129563@1523473221390/The-outdoor-VSAT-equipment-in-full-deployment-GATR-2013.png https://www.researchgate.net/profile/Stella-Parisi/publicati...
- plasticchris 3y agoWhy not put the horn inside the balloon such that it will be in the correct position once inflated?
- mikewarot 3y agoIt's simpler on the outside, less holes to make in the envelope of the balloon.
- cwillu 3y agoEvery wire/tube/whatever you need to be inside the balloon is another place for a seal to fail. If the material of the balloon is transparent to the signal you're looking for (as it must be: the reflector is inside and the the universe you want to look at is outside), then there's no benefit to be had.
- ChuckMcM 3y agoNon-blog-spam link: https://www.nasa.gov/directorates/stmd/nasa-tech-breathes-life-into-potentially-game-changing-antenna-design/ https://www.nasa.gov/directorates/stmd/nasa-tech-breathes-li... Do you have a reference for this? In other channels there have been discussions about this and how it might work. A lot of questions about "hold the outside edge" and "parabola". Specifically if the outside edge is being held by the inflation the interior shape will become a sphere, if the outside edge is rigid like the balloon in the image shows, does it really save weight? A couple of discussions about if you made the "balloon" part sort of like a tube balloon animal where you created interconnected tubes of the backing frame as one balloon that when you inflated formed the shape of a parabola. But neither the press release nor that image suggests anything like that, and positioning the horn would be a challenge. Definitely curious, waiting for the paper.
- uoaei 3y agoFrom the previous HN post[1] about it, I was linked to the company's own page[2] which includes a more precise description of the technology. The reflector is indeed spherical and there is an array of transceivers along the "focal line". [1] https://news.ycombinator.com/item?id=38043955 https://news.ycombinator.com/item?id=38043955 [2] https://www.freefallaerospace.com/nasa-balloon/ https://www.freefallaerospace.com/nasa-balloon/
- orbital-decay 3y agoThanks, the picture instantly explains it. The previous reporting was confusing and clearly missed the whole principle by mixing up spherical and parabolical.
- uoaei 3y agoI think you are conflating two separate designs. The company developing this concept explicitly uses the phrase "spherical reflector" and contrasts it against previous designs based on parabolas. https://www.freefallaerospace.com/nasa-balloon/ https://www.freefallaerospace.com/nasa-balloon/
- itishappy 3y agoI think you're right. Looking through their antennas page shows a lot of similar spherical designs, including the AllSky antenna that's being tested on the same balloon as the inflatable one. They look remarkably similar in design: spherical with a moveable transceiver to be able to steer the beam without moving the antenna. https://www.freefallaerospace.com/antennas/ https://www.freefallaerospace.com/antennas/
- mikewarot 3y agoOk... I stand corrected... interesting that there are two different approaches at play here. So, the moving feed inside a balloon is an interesting twist.